In an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a user equipment (UE) accesses the radio network through an enhanced Node B (eNB). The eNB initiates connections on the air interface, assigns air-interface resources and performs scheduling. The eNBs are connected to a core network via an interface known as S1. The eNBs are also interconnected through an interface known as X2, which allows the eNBs to initiate and complete actions, such as handovers, without having to use higher network authorities to co-ordinate the action.
Femtocells (or “Home” or “Enterprise” eNBs) are small, low-power, indoor cellular base stations for residential or business use. They provide better network coverage and capacity than that available in such environments from the overlying macrocellular network (i.e. the eNBs). In addition, Home or Enterprise eNBs use a broadband connection to receive data from and send data back to the operator's network (known as “backhaul”).
The Home or Enterprise eNB acts as an extension to the existing macro cellular network and provides enhanced network coverage and capacity for all users in range of the Home or Enterprise eNB. In a residential context, this means that the Home eNB will provide access to the network for those resident in that location, as well as for neighbours and passers-by if the macrocellular coverage is poor and if the Home eNB is configured to have “open” access. Any interference between transmissions from the Home eNB and the overlying macrocellular network is mitigated by the ability for user equipments (UEs) to handoff between the Home eNB and the macrocellular network.
It has been suggested that due to the nature of these Home or Enterprise eNBs, there is no need for X2 interfaces to be established between neighbouring Home or Enterprise eNBs or between Home or Enterprise eNBs and the macro eNBs for handover signalling. One reason for this is that if X2 interfaces were provided between neighbouring Home or Enterprise eNBs and between Home or Enterprise eNBs and macro eNBs, then a large deployment of Home or Enterprise eNBs (as is envisaged) would result in a very large number of X2 interfaces to be managed by each Home or Enterprise eNB and particularly by each macro eNB. In addition, due to the nature of the Home or Enterprise eNBs, the population of Home or Enterprise eNBs within a macro eNB can change frequently as Home or Enterprise eNBs are activated and deactivated, so the macro eNBs will often need to reconfigure their connections. This would lead to significant complexity in the macro eNB.
However, there are benefits to having an X2 interface available to Home or Enterprise eNBs. These benefits include the ability to perform faster handovers between the femto and macro layers, the ability to wake Home or Enterprise eNBs when user equipments (UEs) which are registered to use the Home or Enterprise eNB arrive in its vicinity, and the ability to provide interference control between Home eNBs and macro eNBs, and also between neighbouring Home eNBs. In particular, a Home or Enterprise eNB can be provided with an indication of the loading and usage of the macro uplink, which is not available by other means.
Therefore, it has been proposed that X2 interfaces between neighbouring Home or Enterprise eNBs and between Home or Enterprise eNBs and the macro eNBs can be provided using a proxy function that operates between the Home or Enterprise eNBs and macro eNBs. An exemplary system is shown in FIG. 1. Thus, the X2 proxy is connected to each of its Home eNBs through one X2 interface for each Home eNB, and it is connected to each of the macro eNBs that manage cells that overlap one or more of the Home eNBs managed by the X2 proxy by respective X2 interfaces.
According to this proposal, for the direction Home eNB to macro eNB, the X2 proxy performs an “aggregation” function to provide the macro eNB with a complete picture of the Home eNB layer loading. The macro eNB is then expected to take account of the Home eNB layer loading, which adds complexity to the macro eNBs. In addition, there is questionable benefit in providing the macro eNBs with an aggregated X2, given that the various Home eNBs will be experiencing different loading conditions and will have different path loss/shadowing to the particular macro eNBs, which leads to different interference susceptibility between the Home eNBs and macro eNBs.
Therefore, it is an object of the invention to provide an alternative solution for providing an X2 interface between neighbouring Home or Enterprise eNBs and between Home or Enterprise eNBs and macro eNBs.